Test plates for chemical or biochemical analyses, which contain a plurality of individual wells or reaction chambers, are well-known laboratory tools. Such devices have been employed for a broad variety of purposes and assays, and are illustrated in U.S. Pat. Nos. 4,734,192 and 5,009,780, for example. Microporous membrane filters and filtration devices containing the same have become particularly useful with many of the recently developed cell and tissue culture techniques and assays, especially in the fields of virology and immunology. Multiwell plates, used in assays, often utilize a vacuum applied to the underside of the membrane as the driving force to generate fluid flow through the membrane. The microplate format has been used as a convenient format for plate processing such as pipetting, washing, shaking, detecting, storing, etc.
Typically, a 96-well filtration plate is used to conduct multiple assays simultaneously. In the case of multiwell products, a membrane is placed on the bottom of each of the wells. The membrane has specific properties selected to filter or to support biological or chemical reactions. High throughput applications, such as DNA sequencing, PCR product cleanup, plasmid preparation, drug screening and sample binding and elution require products that perform consistently and effectively.
One such filtration device commercially available from Millipore Corporation under the name xe2x80x9cMultiscreenxe2x80x9d is a 96-well filter plate that can be loaded with adsorptive materials, filter materials or particles. The Multiscreen underdrain has a phobic spray applied in order to facilitate the release of droplets. More specifically, the MultiScreen includes an underdrain system that includes a spout for filtrate collection. This spout not only directs the droplets but also controls the size of the droplets. Without the underdrain system, very large drops form across the entire underside of the membrane and can cause contamination of individual wells. Access to the membrane can be had by removing the underdrain. However, assay results are sensitive to liquid collection between the membrane and the underdrain due to membrane weeping. Also, membrane flatness can be problematic depending on the reading technology used. The device also is not compatible with automated robotics equipment such as liquid handlers, stackers, grippers and bar code readers.
A conventional application for the microplate format that does not involve filtration is enzyme linked immuno-spot (ELISPOT) assays. In an ELISPOT assay, for example, the wells of the ELISPOT plate are coated with an antibody that is specific for the cytokine that is being assayed for. The antibody binds to the nitrocellulose or polyvinylidene fluoride (PVDF) membrane portion of the ELISPOT plate. Activated peripheral mononuclear cells are transferred to the plate, and the cytokines are released during an incubation period. The released cytokines bind to and are therefore captured by the specific antibody. The cells and excess cytokines are washed away, and a second antibody also specific for the cytokine of interest that is coupled to an enzyme capable of converting a substrate into an insoluble colored product is added. The substrate is converted into an insoluble product, forming spots or colors that represent the areas of captured cytokines. The spots can be quantitated using a microscope or digital imaging system. The ELISPOT assay provides an effective method of measuring antibody or cytokine production of immune cells on the single cell level.
In applications such as ELISPOT assays where the membrane is not used as a filter, but rather as a substrate upon which a biochemical reaction occurs and is detected, the underdrain not only becomes unnecessary, but also can be problematic. The underdrain both hinders access to the membrane for imaging and can cause the membrane to bow, which also deleteriously effects imaging. In addition, leakage or weeping of liquid through the membrane into the area between the membrane and the underdrain can ruin the assay, and may be dangerous to the user if the samples or reagents involved are biohazards, for example.
The Society for Biomolecular Screening (SBS) has published certain dimensional standards for microplates in response to non-uniform commercial products. Specifically, the dimensions of microplates produced by different vendors varied, causing numerous problems when microplates were to be used in automated laboratory instrumentation. The SBS standards address these variances by providing dimensional limits for microplates intended for automation.
It would therefore be desirable to provide a multiplate format that allows for easy access to the membrane while reducing or eliminating the deleterious retention of liquid under the membrane, loss of membrane flatness, and/or accidental separation of the wells from the tray.
It also would be desirable to provide a multiplate format that is automation compatible.
The problems of the prior art have been overcome by the present invention, which provides a laboratory device design particularly for a multiplate format that includes a plate or tray having at least one well with a support associated with the well, and a removable undercover. The undercover protects the support or membrane from external contamination without causing excessive force on an individual well that can interfere with the membrane""s flatness. The undercover is easily removable to provide access to the support or membrane.
According to a preferred embodiment of the present invention, there is provided a multiwell device including a multiwell plate or tray having a membrane as a support, and an undercover affixed to the underside of the multiwell plate or tray so that the plate or tray and undercover are transportable as a single unit, the undercover being removable from the plate or tray, the multiwell device meeting SBS automation standards even with the undercover in place.